Two major issues: spending per student in the US is in fact very split between wealthy and poor districts. Philadelphia spends $11,000 per student per year, almost $10,000 less than nearby Lower Merion, and is constantly short of funds. Not that there isn’t waste in Philly’s system, but money certainly isn’t easy to come by for teachers.

Second, the other countries which do well tend to have strong, generous social support networks. My guess (as a former teacher) is that schools there don’t have to provide health care, counseling, food, etc to students who have trouble getting them at home. One huge difference between my experience going to school and my experience teaching was that, by and large, the kids I went to school with got glasses when they needed them, and if they fell way behind in reading or math, their parents noticed (were equipped to notice by their own educational success) and got them tutoring or other assistance (because they had either time or money with which to provide those things).

There are still huge problems within our educational system that are matters of educational policy rather than social policy more broadly defined: we lack a unified set of national standards, the standards we do have (especially in math, though this may also be true in other subjects where I know the debates less well) are less rigorous and more connected to rote memorization than the standards in other countries, and teachers have far less prep and development time than teachers in, for example, Japan.

I’m routinely astonished, though, by the number of non-educators (and sometimes educators) who think that failing students is somehow the key. This always, always comes up in comments on articles about education, and usually some version of this will also come up in a professional development workshop. Yes, students need accountability, and yes, it makes your job a lot harder when students don't know the earlier material. But making them repeat the same material in the same context without additional supports doesn’t help - it just leads to a bored, frustrated kid who thinks he or she has already learned this (and has, in the sense of having sat in a classroom while it was being taught). The evidence also just doesn't support a claim that making students repeat a grade improves their achievement - mostly it makes them more likely to drop out, and lowers over-all achievement. You can’t just keep doing the same thing and expect different results.